Lead acid storage battery and method of bonding battery cell terminal posts and bushings

ABSTRACT

An improved method of bonding battery cell terminal posts to cover bushings is disclosed. The battery cell terminal posts are made of lead alloy material and the cover bushings are made of solder alloy material having a significantly lower melting point than the terminal posts. The bushings are bonded to the terminal posts by heating the terminal posts and bushings to a temperature above the melting point of the material of the bushing, but below the melting point of the material of the post, to effect a secure and leak proof connection without melting of the terminal posts and with lesser chance for damage to the plastic cover. The plastic cover further includes integrally formed annular mold sections in the form of upstanding bosses which completely surround respective bushings and posts.

RELATED APPLICATION

This is a divisional of Ser. No. 08/903,466, filed Jul. 30, 1997, nowU.S. Pat. No. 5,905,002 continuation-in-part of my application Ser. No.08/799,294 filed Feb. 13, 1997, now U.S. Pat. No. 6,008,480, thedisclosure of which is incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates generally to batteries, and moreparticularly, to an improved method for bonding battery cell terminalposts to respective bushings in the battery casing to form terminals ofthe completed battery.

BACKGROUND OF THE INVENTION

In the manufacture of lead acid industrial and automotive storagebatteries, it is customary to mold lead bushings in the plastic cover ofthe battery and to thereafter fuse the bushings to posts of the batterycell assemblies. Typically both the posts and bushings must be heated totemperatures above their melting points such that there is a fusion ofthe materials of the two components.

It has long been the practice to melt the ends of the posts and bushingsby means of manually operated acetylene torches. Not only does suchmanual acetylene torch burning of the posts and bushings fail to lenditself to use in fully automated battery production lines, the qualityand depth of the fused areas cannot be uniformly controlled. Moreover,particular care must be taken in not melting or otherwise damaging theportion of the plastic cover immediately adjacent the bushing, which canrender the battery defective or sufficiently weaken the seal and supportbetween the plastic cover and bushings as to create a potentiallydangerous condition during use of the battery. Such acetylene torchburning, furthermore, is tedious and potentially harmful to the workingenvironment, and it is difficult to control the flow of melted lead,resulting in unsightly irregularities in the surfaces of the finishedbattery terminals.

While various proposals have been made for automatically fusing batteryterminal posts and cover bushings by means of acetylene torch heating,tungsten inert gas welding, electrical resistance heating, andelectrical induction heating, such proposals all have faced variousdrawbacks, including the inability to obtain reliable fusion depthswithin the requisite processing time, undesirable melting of the coverabout the bushings, unacceptable appearance of the finished terminals,or the necessity for utilizing auxiliary molds to control melted leadand achieve acceptable terminal appearance.

OBJECTS AND SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method of bondingbattery cell posts and casing bushings in forming battery terminalswhich can be carried out at lower heating temperatures than heretoforepossible, and hence, reduces the possibility for melting of the plasticcover or damaging the seals between the bushings and the plastic cover.

Another object is to provide a method as characterized above that can becarried out without heating the battery cell posts above their meltingtemperature. A related object is to provide such a method that can beoptimally controlled to more reliably prevent melting and damage of theplastic cover.

A further object is to provide a lead acid storage battery in whichposts and cover bushings are bonded to form the battery terminalswithout the necessity for fusing and intermixing materials of the twocomponents typical of the prior art.

Yet another object is to provide a lead acid storage battery of theabove kind in which the cover bushings are formed of a solder materialhaving a substantially lower melting temperature than the lead alloy ofthe battery cell posts to which they are bonded.

Another object is to provide a lead acid storage battery in which thecover has integrally formed mold sections completely surrounding theposts and bushings to form dams for the melted bushings during bondingand which mold the terminals in finished form.

A further object is to provide a battery of the foregoing type in whichthe integral mold sections of the cover aesthetically and protectivelycontain the battery terminals for the life of the battery.

Still another object is to provide such a lead acid storage battery inwhich the integral mold sections of the cover provide an alignmentreference for positioning induction heating coils during bonding of theterminal posts and bushings for enhancing uniformity of the resultingbonds in automated battery production lines.

Yet another object is to provide a battery of the foregoing type inwhich the integral mold sections are bonded to a final outer cover ofthe battery to form a redundant seal between the cover and bushings forlong term reliable usage.

Other objects and advantages of the invention will become apparent uponreading the following detailed description and upon reference to thedrawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective of a lead acid storage battery embodying thepresent invention;

FIG. 2 is an enlarged fragmentary section of one of the fused terminalsof the battery shown in FIG. 1, taken in the plane of line 2—2;

FIG. 3 is an enlarged fragmentary section showing a battery inoperatively positioned relation to an induction heating coil of theinduction heating apparatus shown in FIG. 4, prior to bonding of theterminal post and cover bushing;

FIG. 4 is a front elevation view of the illustrated induction heatingapparatus;

FIG. 5 is a fragmentary section of an alternative method of bonding thebushing and post; and

FIG. 6 is a fragmentary selection of another embodiment of a lead acidstorage battery according to the present invention.

While the invention is susceptible of various modifications andalternative constructions, certain illustrated embodiments thereof havebeen shown in the drawings and will be described below in detail. Itshould be understood, however that there is no intention to limit theinvention to the specific forms disclosed, but on the contrary, theintention is to cover all modifications, alternative constructions andequivalents falling within the spirit and scope of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring now to FIGS. 1 and 2 of the drawings, there is shown anillustrative lead acid storage battery 10 having terminals 11 on a topside thereof. The illustrated battery 10 includes a case 12, preferablymade of plastic, containing a plurality of battery cell elements thatare electrically coupled to the terminals 11.

During manufacture of lead acid storage batteries of such type, it iscustomary to assemble onto the case 12 a cover 20 having terminalbushings 21 mounted therein with terminal posts 22 of the battery cellelements extending upwardly through respective bushings 21, as depictedin FIG. 3. The terminal posts 22, which may be made of a conventionallead alloy, have a slight upward external taper and are positionableinto respective tapered axial openings 24 of the bushings 21 shapedgenerally complementary to the terminal posts 22. The lowermost end ofeach bushing opening 24 has an outwardly flared chamfer 25 for guidingthe respective terminal post 22 into proper seating relation to thebushing 21 during assembly of the cover 20 onto the case 12. Forreliably supporting the bushings 21 in the cover 20, the bushings 21each have a ribbed outer peripheral mounting portion 26 adapted toprovide a strong mechanical connection with the plastic cover 20, whileforming an effective seal about the periphery of the cover and bushing.

For bonding the terminal posts 22 and bushings 21, an induction heatingapparatus 27 is provided that preferably is part of an automatedproduction line having a conveyor track 28 upon which batteries 10 to beassembled are moved through successive operating stations (FIG. 4). Aplurality of selectively actuatable pivotal stops 29 are mounted on anunderside of the track 28 for stopping the batteries at predeterminedoperating stations, including an induction heating station, as shown inFIG. 4. An elevator 30 operated by an air cylinder 31 successively liftsthe battery 10 off the track 26 at the induction heating station toposition the terminal posts 22 and bushings 21 thereof into operativerelation for an induction heating cycle and therefore returns thebattery to its lowered position on the track 28 for further transfer andprocessing.

The induction heating apparatus 27, which is described in more detail inthe above referenced U.S. Pat. No. 6,008,480, includes a plurality ofinduction heating coils 35 that are operable for effecting simultaneousbonding of a corresponding number of terminal posts 22 and bushings 21of batteries being processed. The coils 35 are mounted on a T bus 36supported in cantilever fashion from a high voltage, induction heatinggenerator 38, for example, having a 30 kilowatt capacity at 450 kHz.

Each inducting heating coil 35 is formed from a respective continuouslength of copper tubing, which in this case defines an annular coil turn39 and a pair of upstanding mounting legs 40 adjustably supported by theT bus 36 for selective vertical positioning along a Z or vertical axis.While in the illustrated embodiment the coils 35 are shown as having asingle annular turn 39, it will be understood that the coils may beformed with a multiplicity of helical turns. For purposes herein, theterm “coil” encompasses inducting heating coils having one or moreturns.

In accordance with an important aspect of the invention, the bushingsand posts can be bonded at significantly lower induction heatingtemperatures than heretofore possible. More particularly, the bushingsare made of a material having an appreciably lower melting temperaturethan the terminal posts, and during an induction heating cycle, theterminal posts and bushings are heated to a temperature range above themelting point of the bushings, while remaining below the melting pointof the terminal posts. To this end, in the illustrated embodiment, thebushings 21 are made of a solder alloy material, preferably having amelting temperature at least about 100 degrees F. lower than the meltingtemperature of the lead alloy material of the terminal posts 22.Assuming that the terminal posts are made of a conventional lead alloymaterial, such as Pb and Sb and/or Sn alloys, which have meltingtemperatures of about 600 degrees F., a solder material such as aeutectic (minimum melting point) alloy of lead and antimony may be used,which has a melting point of about 477 degrees. It will be understoodthat other solder alloy materials could be used so long as the materialis not subject to extensive corrosion during prolonged exposure tobattery strength sulfuric acid electrolyte and will not contaminate thelead acid battery chemistry.

During an induction heating cycle, it has been unexpectedly found thatthe terminal posts 22 and bushings 21 need only be heated to atemperature above the melting point of the solder alloy of the bushings21 to achieve secure bonding between the bushings 21 and the terminalposts 22. Suitable fluxes of a known type may be used at the terminalpost-bushing interface to enhance solder bonding between the bushing andpost. While the resulting bonds are not fused in the sense of the priorart wherein melted materials of the bushing and terminal post intermixand fuse together, the resulting bond is sufficient to achieve amechanically strong and leak-free connection between the post andbushing that will withstand long term usage of the battery.

It will be understood by one skilled in the art that the bushings 21need not be designed for current carrying capabilities. Instead, thebattery cell terminal posts 22 can be sized for conducting the ratedoperating current of the battery during usage In the illustratedembodiment, to enhance current conduction through the terminal posts 22,each terminal post 22 has a cylindrical copper insert 42 threadedconcentrically into an upper end thereof.

By appropriate selection of lead and solder alloy materials for thebattery terminal posts 22 and bushings 21, it will be understood thatbonding between the two elements can be optimally and uniformlycontrolled even in an automated production line. Since such bonding canbe quickly effected at induction heating temperatures lower thanheretofore possible, batteries can be produced with increasedproductivity and with lesser likelihood of damage to the plastic coveror the seal between the plastic cover and bushing.

In accordance with a further aspect of the invention, the battery coverhas integrally formed mold sections 45 that completely surround eachbushing 21 and post 22 to define a dam 46 for controlling meltedmaterial of the bushing 21 during an induction heating operation and forforming the battery terminal in finished shape. In the illustratedembodiment, each integral mold section 45 is in the form of anupstanding annular boss or lip substantially concentric with the post 22and bushing 21 to be bonded. Each mold section 45 protrudes upwardly arelatively small distance L, such as on the order of 0.060 inches, fromthe top surface of the bushing 21. Since the mold sections 45 completelyencompass the bushings 21 and posts 22, they both contain meltedmaterial of the bushing during a bonding operation and mold the batteryterminals in finished form. With the mold sections 45 being an integralpart of the cover 20, there also is no need to deliver or otherwiseprovide a separate auxiliary molds to the battery during the inductionheating operation. Furthermore, being an integral part of the batterycover, the mold sections 45 aesthetically and protectively contain theformed battery terminals throughout the life of the battery. While theillustrated mold sections 45 are annular bosses concentric to theterminal posts 22 and bushings 21 to be bonded, it will be understoodthat the mold sections may have other, non-concentric configurations.

In keeping with the invention, the integral mold sections of the coverfurther define a reference for reliable and repeatable location of theinduction heating coils 35 with respect to the battery during inductionheating cycles for facilitating uniform bonding of the terminal postsand bushings even in automated battery production lines. As depicted inFIG. 3, the annular mold sections 45 of the cover 20 each define a flatupper reference surface 48 for engagement with a respective inductionheating coil turn 39, such as upon upward movement of the battery 10 bythe elevator 30. Hence, when the battery 10 is moved into operativerelation to the induction heating apparatus 27, each reference surface48, as defined by the respective integral mold section 45, is broughtinto engaging relation with an underside of a respective annular coilturn 39 for establishing a repeatable, redetermined position of thebushing 21 and the terminal post 22 relative to the coil. In theillustrated embodiment, in such seated position each coil is spacedslightly above the upper end of the respective bushing 21, with the post22 extending partially, in this case about midway, into the annularopening defined by the coil.

With the coil turn 39 in such predetermined spaced relation to both thebushing 21 and terminal post 22, upon energization of the inductionheating generator 38, current flow through the T bus 36 and coils 35induces substantially instantaneous and uniform high voltage heating inthe bushings 21 and posts 22 disposed in coaxial relation to the coils.It will be understood by one skilled in the art that by selectiveoperation of the induction heating apparatus 27, such induction heatingcan be controlled to consistently heat the bushings 21 to a narrowtemperature range that is above the melting point of the solder alloymaterial of the bushing, but below the melting point of the lead alloymaterial of the terminal post. Because of the substantially uniformorientation of each coil 35 of the induction heating apparatus 27relative to the bushings 21 and terminal posts 22, bonding of thebushings and terminal posts can be uniformly effected without damage tothe surrounding plastic material of the cover 20. While in theillustrated embodiment the integral mold sections 45 of the batterycover 20 are described in connection with bonding of solder alloybushings to lead alloy terminal posts, it will be understood that suchintegral mold sections of the cover are equally advantageous when fusingconventional lead alloy bushings and posts by induction heating.

Referring now to FIG. 5, there is shown an alternative embodiment of theinvention wherein items similar to those described above have been givensimilar reference numerals with distinguishing suffix “a” added. In thisembodiment, the upstanding mold sections 45 a of the battery cover 20 aare designed to fit concentrically within the induction heating coilturn 39 a for locating the battery terminal posts 22 a and bushings 21 ato be bonded in the horizontal plane, i.e. X and Y directions, as wellas in the vertical, i.e., Z direction. The mold sections 45 a preferablyare slightly smaller in diameter than the annular turn 39 a of the coilfor enabling easy positioning of the mold sections 45 a into the annularcoil turns 39 a in an automated production line, while establishing areference for the terminal posts and bushings in the X and Y directions.It will be understood that the induction heating coil may haveappropriate probes that are engageable with a top surface of the cover20 a for establishing predetermined vertical positioning of the batterywith respect to the coil.

Referring now to FIG. 6, another alternative embodiment of a battery inaccordance with the invention is shown wherein items similar to thosedescribed above have been given similar reference numerals with thedistinguishing suffix “b” added. In this embodiment, the bushings 21 bto be bonded are mounted in an intermediate cover 20 b of the batteryand an outer or final cover 50 is mounted on the battery case invertically spaced relation above the intermediate cover 20 b. Theintermediate cover 20 b in this case has integral formed mold sections45 b extending upwardly into sealing contact with the final or outercover 50 to provide a redundant hermetic seal about the formed terminal.It will be understood that after induction heating bonding or fusion ofthe bushings and post, as previously described, the final cover 50 maybe positioned onto the battery case and bonded to the upper perimeter ofthe mold sections 45 b, such as by sonic welding. The upstanding moldsections 45 b again provide cavities 46 b for the molten bushingmaterial during induction heating, protectively contain the finishedbattery terminals, define a reference for the induction heating coils,and in addition, provide a redundant hermetic seals about the bushingand terminal posts in the finished battery.

From the foregoing, it can be seen that since the terminal posts andbushings need only be heated above the relatively lower melting point ofthe bushings, the induction heating operation can be carried out atlower temperatures than heretofore possible, thereby reducing thepossibility for damage to the plastic cover. Since the integral formmold sections of the cover completely surround, contain and shape anymelted material of the bushing during the bonding operation, there is nonecessity for the delivery and handling of separate molds. The methodfurther lends itself to efficient and economical manufacture inautomated production lines.

What is claimed is:
 1. A method of making a lead acid storage batterycomprising providing a battery case with a plurality of battery cellshaving at least one terminal post, providing a battery cover having abushing supported therein and an integral mold section of the covercompletely surrounding the bushing and extending upwardly at least to anupper perimeter of said bushing, positioning the cover on the batterycase with said terminal post extending upwardly through said bushing,locating the battery case with the cover mold section in predeterminedrelation to an induction heating coil, energizing said induction heatingcoil to induce current flow through said post and bushing to melt atleast a portion of the bushing and secure the bushing to the post withthe mold section retaining melted material of the bushing.
 2. A methodof making a lead acid storage battery comprising providing a batterycase with a plurality of battery cells having at least one terminal postmade of lead alloy material, providing a cover having a bushingsupported therein made of a material having a melting point at leastabout 100 degrees F. less than the melting point of the lead alloymaterial of said post, and heating the terminal post and bushing to atemperature above the melting point of said bushing but below themelting point of the post to bond the bushing to the post with a secureleak free joint.
 3. The method of claim 2 including positioning the postand bushing in predetermined relation to an induction heating coil, andheating said post and bushing by energizing the coil to induce currentflow through said post and bushing.
 4. The method of claim 3 includingproviding the cover with an integral upstanding mold section completelysurrounding the bushing, and containing melted material of said bushingin said mold section during heating to form the bushing in final shape.5. A method of making a lead acid storage battery comprising providing abattery case with a plurality of battery cells having at least oneterminal post made of lead alloy material, providing a cover having abushing supported therein made of a solder alloy material having amelting point below the melting point of the material of said terminalpost, and heating the terminal post and bushing to a temperature abovethe melting point of said bushing but below the melting point of thepost to bond the bushing to the post with a secure leak free joint.
 6. Amethod of making a lead acid storage battery comprising providing abattery case with a plurality of battery cells having at least oneterminal post, providing a battery cover having a bushing supportedtherein and an integral upstanding mold section of the cover completelysurrounding the bushing, positioning the cover on the battery case withsaid terminal post extending upwardly through said bushing, locating thebattery case with the cover mold section in predetermined relation to aninduction heating coil by engaging said mold section with said coil,energizing said induction heating coil to induce current flow throughsaid post and bushing to melt at least a portion of the bushing andsecure the bushing to the post with the mold section retaining meltedmaterial of the bushing.
 7. The method of claim 6 including locatingsaid battery case by engaging a top surface of said mold section withsaid coil.
 8. The method of claim 6 including locating the battery caseby raising the battery case upwardly to engage a top surface of saidmold section with an underside of said coil.
 9. A method of making alead acid storage battery comprising providing a battery case with aplurality of battery cells having at least one terminal post, providinga battery cover having a bushing supported therein and an integralupstanding mold section of the cover completely surrounding the bushing,positioning the cover on the battery case with said terminal postextending upwardly through said bushing, locating the battery case withthe cover mold section in predetermined relation to an induction heatingcoil by positioning said mold section within said coil, energizing saidinduction heating coil to induce current flow through said post andbushing to melt at least a portion of the bushing and secure the bushingto the post with the mold section retaining melted material of thebushing.
 10. The method of claim 9 including locating said battery caseby raising said case upwardly to position said mold section within saidcoil.
 11. A method of making a lead acid storage battery comprisingproviding a battery case with a plurality of battery cells having atleast one terminal post, providing a battery cover having a bushingsupported therein and an integral upstanding mold section of the covercompletely surrounding the bushing, positioning the cover on the batterycase with said terminal post extending upwardly through said bushing,locating the battery case with the cover mold section in predeterminedrelation to an induction heating coil, energizing said induction heatingcoil to induce current flow through said post and bushing to heat saidbusing to a temperature above the melting point of the material of thebusing but below the melting point of the material of the post so as tomelt at least a portion of the bushing and secure the bushing to thepost with the mold section retaining melted material of the bushing. 12.A method of making a lead acid storage battery comprising providing abattery case with a plurality of battery cells having at least oneterminal post, providing a battery cover having a bushing supportedtherein and an integral upstanding mold section of the cover completelysurrounding the bushing, positioning the cover on the battery case withsaid terminal post extending upwardly through said bushing, locating thebattery case with the cover mold section in predetermined relation to aninduction heating coil, energizing said induction heating coil to inducecurrent flow through said post and bushing to melt at least a portion ofthe bushing and secure the bushing to the post with the mold sectionretaining melted material of the bushing, positioning an outer cover onsaid case in vertically spaced relation above the cover within whichsaid bushing is supported following bonding of said bushing and saidpost, and bonding said outer cover to the top of said mold section.